An unmanned X-51 WaveRider was expected to reach Mach 6 Tuesday when it was dropped by a B-52 bomber and took flight off the Southern California coast near Point Mugu. But just what sort of technology would allow it to travel 3,600 miles per hour? It's called a scramjet engine.
A Supersonic Combustion Ramjet (scramjet) uses oxygen from the atmosphere to create the combustion in its engine, instead of from an onboard tank according to NASA. This means the aircraft is "smaller, lighter and faster." So fast, NASA says that researchers think it will reach 15 times the speed of sound making an 18-hour flight from New York City to Tokyo only 2 hours long. The Los Angeles Times reports a trip from Los Angeles to New York would only take 46 minutes.
Another interesting feature of the scramjet engine is that it has no moving parts.
This animation from Space.com shows how the X-51's scramjet engine works:
Aviation History has more on how the engine functions and how it differs from other engines:
Air entering the intake of a supersonic aircraft is slowed by aerodynamic diffusion created by the inlet and diffuser to velocities comparable to those in a turbojet augmentor. The expansion of hot gases after fuel injection and combustion accelerates the exhaust air to a velocity higher than that at the inlet and creates positive push.
The scramjet differs from the ramjet in that combustion takes place at supersonic air velocities through the engine. It is mechanically simple, but vastly more complex aerodynamically than a jet engine. Hydrogen is normally the fuel used.
Designed by Boeing Co., the X-51 is intended to allow the Pentagon to deliver strikes around the globe within minutes.
During a test last year, it fell for about four seconds before its booster rocket ignited. The aircraft failed to separate from the rocket and dropped into the ocean. Engineers hope X-51 sustains its top speed for 300 seconds in this latest test -- twice as long as it's gone before. After this test flight, the L.A. Times reports WaveRider will break up upon impact with the Pacific Ocean, which is part of the plan.
"The X-51 is a technology feeder to larger, more sustained flight times," Darryl Davis, president of Boeing Phantom Works, told the L.A. Times. "The hope is to advance the state of the art."
The L.A. Times reports NASA and the Pentagon's DARPA program funding three national centers in hypersonic flight research. The Pentagon itself is funding six programs, spending $10 billion in the last decade on the hypersonic technology.
Update: According to a tweet by Wired's Danger Room (via Business Insider), it appears the Tuesday test flight failed. Danger Room doesn't cite where it received this information.
Reuters reported later on Wednesday the X-51 broke apart within minutes of its test beginning and fell into the Pacific. It notes a problem with the control fin as being the cause of the failure. Reuters goes on to report an Air Force statement noting that one more X-51 remains and it is not decided "when or if that vehicle will fly at this time."
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- DARPA Reveals Why Its Hypersonic Glider Failed Last Summer
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The Associated Press contributed to this report.